Devices and systems for detecting explosives and other terrorist-type devices are installed in virtually every United States airport. Devices for detecting explosive systems are referred to as Explosive Detection Systems (EDS). These systems are based upon x-ray computed tomography (CT) systems and produce images of x-ray attenuation of the interior of luggage, packages and the like that are reviewed for evidence of hidden explosives. The devices in which the luggage, packages, and other items are passed through are also called “scanners.”
There currently are not any standard methodologies or corresponding hardware for evaluating how well an EDS is performing consistently over time. Currently, CT phantoms of various sizes and shapes are used to determine one performance measure or another, at one location or another, in the field of view. There currently are not any devices or systems for measuring performance across the entire field of view of the EDS, nor of determining image resolution and contrast sensitivity quantitatively with a single test phantom.
The standard test method for measuring the performance of computer tomography systems is set forth in American Society for Testing and Materials (ASTM) E1695. This test method provides instruction for determining the spatial resolution and contrast sensitivity in x-ray and γ-ray computed tomography images. The determination is based on examination of the CT image of a uniform disk of material. The spatial resolution measurement is derived from an image analysis of the sharpness at the edge of the disk. The contrast sensitivity measurement is derived from an image analysis of the statistical noise at the center of the disk.
There is a need for a simple and efficient test measuring device and process which can assist in the calibration of EDS systems in a quicker and easier manner, and which provides uniform and accurate results. There also is a need for measuring performance of EDS systems and devices, particularly across the entire field of view and with a single test device.